<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
            .box{
                position: relative;
                padding-top: 8px;
            }
            .con{
                width: 200px;
                height: 100px;
                border: 1px skyblue solid;
                border-radius: 3px;
                background-color: skyblue;
            }
            .con-ret{
                border: 7px solid transparent;
                border-bottom-color:skyblue; 
                position: absolute;
                left: 10px;
                top:-6px;
            }
        </style>
    </head>
    <body>
        <div class="box">
            <div class="con-ret"></div>
            <div class="con"></div>
        </div>
    </body>
    
</html>